Effect Of Inducer Geometric Parameters On Cavitation Characteristics Of LNG Submersible Pump

Cavitation refers to the process of forming vapor bubbles in the low pressure region.The cavitation problem of hydraulic machinery is unavoidable and affects the normal operation.First,the cavitation causes the performance to drop which seriously affects the pump.Second,the cavitation is likely to create material damage of solid surface when the cavity is broken.Third,cavitation not only effects the normal state of fluid flow.It also bring about the unsteady characteristics and dynamic response characteristics,which can influence oscillations in the flow and pressure in the pump,causing damage to the structure of the pump and piping.In engineering practice,cavitation has become one of the main causes.More researches show that the setup of the inducer in front of the centrifugal pump can effectively improve the cavitation performance.The fluid enters the inducer and is pressurized to increase the inlet pressure of the impeller.As a special cryogenic pump,it is the core problems how to improve cavitation performance of LNG submersible pump.Based on the combination of numerical calculation and experimental verification,a method of changing the inlet hub ratio of the inducer and changing the geometry of the section of the inducer blade is proposed.The cavitation development process,the cavitation instability and the centrifugal pump pressure pulsation characteristics are studied in depth.The main research contents of this paper are:1.The cavitation evolution process of the centrifugal pump was studied by analyzing the cavitation distribution the model pump,the static pressure distribution of the inducer suction surface and the inducer axis velocity vector distribution under different cavitation numbers.The study shows that the cavitation first appears at the inlet rim of the inducer.With the development of cavitation,the cavity inside the inducer extends toward the exit,and forms a self-excited pressure oscillation.The pressure presents a high frequency pulsation phenomenon at the inducter outlet and the impeller inlet.When the cavitation number drops to the critical cavitation number,the wake vortex cavitation occurs at the exit of the inducer which has an influence on the impeller.In the severe stage,the cavity fills the entire the inducer path,the centrifugal pump operating conditions are broken,and the vibration and noise increase sharply.2.Five sets of centrifugal pumps with different inducer inlet hub ratios(?=0.260,?=0.289,?=0.318,?=0.274 and ?=0.303)are used for analysis and the influence of different inlet hubs on the cavitation characteristics of the centrifugal pump is studied.The results show that with the increase of the inducer inlet hub ratio,the velocity of axial plane component,at the inlet of the rim is increased.On the basis of the same blade placement angle,the positive angle of the inlet flow of the blade is reduced,the liquid is de-flowed at the inlet of the suction surface of the blade,and the cavitation performance of the centrifugal pump is reduced.However,changing the inlet hub of the inducer has less effect than the external characteristics of the centrifugal pump.Therefore,in order to obtain a higher cavitation performance,the inducer inlet hub ratio can be reduced within an appropriate range in design of inducer.The cavitation performance of with the inducer inlet hub ratio of 0.260 is optimal.3.Four sets of centrifugal pumps with different inclination angles(?=+6°,?=+3°,?=0° and ?=-3°)are used for analysis and the influence of the section angle of the inducer blade on the cavitation characteristics of the centrifugal pump was studied.The results show that the section angle of the inducer blade changes the static pressure distribution of the suction surface.The inversion of the inducer blade causes a high kinetic energy region at the impeller exit.The cavitation vortex at the impeller exit falls off and adheres to the blade pressure surface,causing the flow velocity at the impeller exit to be disordered,and the centrifugal pump performance is reduced.Under the same static pressure condition of the inducer exit,the inlet dynamic pressure is the largest when the inducer is inclined forward by ?=+3°,and the energy conversion of the inducer are optimal.However,if the angle is inclined too much,the too early turning time is not conducive to the improvement of the cavitation performance.Therefore,when the inducer blade section angle is ?=+3°,the pump cavitation performance is optimal.